groundless vs idle

groundless is not a noun while idle is a noun.

Word	Noun	Adjective	Verb	Adverb
groundless	No	Yes	No	No
idle	Yes	Yes	Yes	No

As adjectives, groundless and idle are synonyms defined as:

Other synonyms of groundless include baseless, unfounded, unwarranted, wild.

groundless (noun)	idle (noun)
	the state of an engine or other mechanism that is idling

groundless (adjective)	idle (adjective)
without a basis in reason or fact	not in action or at work
	silly or trivial
	not in active use
	lacking a sense of restraint or responsibility
	not having a job
	not yielding a return
	without a basis in reason or fact

groundless (verb)	idle (verb)
	run disconnected or idle
	be idle; exist in a changeless situation